Electrophotographic imaging processes may be implemented in numerous device configurations (e.g., printer, copier, facsimile, etc.) to form hard images upon media, such as paper. An entirety of a photoconductor may be charged by an initial electrical charge, and thereafter selected portions of the photoconductor may be selectively discharged to form a latent image. The latent image may be developed using a marking agent such as toner in a solid process or liquid ink in a liquid process.
In some liquid electrophotographic imaging devices available from Hewlett-Packard Company, the photoconductor may be charged by three sets of double scorotrons to about approximately −1000V. In other configurations, a charge roller has been demonstrated as an alternative means of charging a photoconductor. A single charge roller has been observed to provide adequate electrical charge with the associated benefits of saving space along a surface of the photoconductor as well as a reduction in maintenance.
Some charge rollers are made of a conductive elastomeric material, commonly urethane, molded over a metal core. The charge roller may be lightly pressed against a photoconductor surface to maintain a constant footprint and therefore provide more consistent charging. In some configurations, steady pressure may not be desirable to maintain a constant footprint. For example, some photoconductor configurations have a seam region wherein a photoconductor sheet is inserted into a drum surface and attached. The drum may have a depression in a seam region so that the seam region of the photoconductor does not stick out farther than the radius of the photoconductor and be subject to mechanical damage. However, in a liquid electrophotographic implementation, imaging oil may accumulate within the seam region of the photoconductor. Print defects may result in hard output if a charge roller picks up oil from the seam region and deposits it on other portions of the surface of the photoconductor. In dry electrophotographic processes, potentially damaging electrical arcing may occur if the charge roller enters the seam region of the photoconductor.
Disks or bearers may be attached to opposite sides of a photoconductor drum to provide a convenient reference at a fixed distance from the drum center over the seam. Hard wheels or drivers attached to a shaft of the charge roller may be aligned with the bearers to prohibit the charge roller from dipping into the seam region.
Associated drawbacks exist with the utilization of disks and drivers. For example, the drive diameter is closely matched to a diameter of the charge roller. With a force being applied to the charge roller sufficient to have the drivers ride upon the bearers, the charge roller surface may not maintain an adequately uniform contact patch due to runout of the wheels and the charge roller. If the drivers are too large relative to the charge roller, contact of the charge roller with the photoconductor surface may be intermittent or absent. On the other hand, if the drivers are too small relative to the charge roller, the charge roller may penetrate the seam to a sufficient degree to contact the accumulated imaging oil. In addition, elastomeric material of the charge roller may swell in the presence of imaging oil or moisture to a degree greater than the drivers so that the drivers and the charge roller are out of alignment. Environmental conditions may vary from a desired specification if a imaging device is out of operation for an extended period of time and the time to re-equilibrate the charger roller to a proper diameter may be unacceptably long.
At least some aspects of the disclosure provide improved apparatus and methods for generating hard images.